With a few important exceptions, polymeric materials offer excellent resistance to inorganic
acids. For example, taking sulphuric acid as reasonably representative of the class, Table
5.7 lists the recommended maximum concentrations and temperatures for some common
rubbers and plastics. As acids promote degradation via hydrolysis the exceptions include
those polymers that are known to be the least hydrolytically stable such as thermoplastic
polyesters, Nylons, polyurethanes, silicones, and polycarbonates. The least resistant polymer
in common use and the one most likely to suffer from acid induced stress corrosion cracking
is acetal. Cases 5.6.4, 5.6.5 and 5.6.10 illustrate the weakness.
The premature failure of GRP products is most frequently traced to the phenomenon
known as stress corrosion cracking (SCC) and the fluid responsible is invariably acidic.
The principal degradation interaction is between the fluid and the fibres. The composition
of glass fibres is as shown in Table 5.8, a mixture of oxides dominated by silicon. E glass